In electrical networks, such as in motor vehicle electrical systems, as a rule, several electrical users are supplied with power by one electrical energy storage device, such as a battery. In order to perform energy management and user management, in which users, depending on requirements, may be automatically switched on and off, knowledge of the capacity of the energy storage device is of essential importance. If the capacity of the energy storage device is known, especially the load that may still be drawn before undershooting a requisite minimum capacity, such as for an engine start, then, even before a short supply sets in, use-reducing or capacity-increasing measures may be introduced, such as switching off certain users, and thus a failure of the electrical supply may be prevented.
In order to estimate the capacity of the energy storage device, it is known that one may use mathematical models that describe the electrical properties of the energy storage. While taking into account current operating variables of the energy storage, such as a current battery voltage UBatt, the current battery current IBatt and the current battery temperature TBatt, the capacity of the energy storage device may be estimated, with the aid of the mathematical models. A device, known from the related art, for determining the load that may be drawn from an energy storage, is shown in FIG. 1.